1. Field of the Invention
The present invention relates to an ophthalmic image sensing apparatus used in an opthalmologist's office etc.
2. Related Background Art
Up to now, in fundus cameras, what are disclosed in Japanese Patent Application Laid-Open No. H05-095902, Japanese Patent Application Laid-Open No. H08-033610, and Japanese Patent Application Laid-Open No. H08-150121 are methods of providing a mechanism of providing a focus index projection barrel which is constituted of an index for focusing detection, a light source illuminating this index, and a projection optical system which has a deflection prism for projecting index images on a fundus of an eye to be examined from different locations of a pupil, and a micro mirror which branches an optical path with a fundus illumination optical system, and of both the micro mirror and focus index projection barrel moving in a direction of an optical axis with interlocking with the focus adjustment of an image sensing optical system, and a mechanism of the micro mirror retreats out of the optical path at the moment of image sensing, and of focusing the fundus of eye with looking at the index images projected on the fundus of eye.
In addition, methods of providing a minute prism in an illumination optical system, projecting a slit image illuminated by fundus observation light on the fundus of eye, and performing focus adjustment are disclosed in Japanese Patent Application Laid-Open No. H06-142050 and Japanese Patent Application Laid-Open No. S54-054494.
Since the above-mentioned conventional methods each must move a whole focus index projection barrel, which is provided with being branched from a fundus illumination optical system, in a direction of an optical axis, it is necessary to secure a large space, and hence, it is difficult to downsize an apparatus. In addition, there are problems that cost is high because of necessity of long adjustment time due to a large parts count, and assembly operation, such as angle adjustment of a micro mirror, and alignment between an index image and a micro mirror, is complicated. Furthermore, there is another problem that a slack wire is worn because the light source where wires are connected is moved.
Moreover, the method of providing a minute prism in the above-mentioned illumination optical system has a problem that it is hard to perform focus adjustment since a focus index portion becomes darker than a surrounding fundus region because of decentering the fund illumination light by a prism and projecting a focus index, or it is user-unfriendly since it is not possible to adjust light intensity independently because fundus illumination and focus index illumination are performed by one light source.
In addition, in fundus image sensing in a mass health examination, an examinee's look is adjusted and image sensed so that a just middle position between an optic disk and a yellow spot may become a center of a screen. Hence, it is necessary to guide this yellow spot in a position, which is decentered from an optical axis, and to take a picture. Nevertheless, it is necessary to change a position of a fixation target at the time of taking a picture of a right eye and at the time of taking a picture of a left eye since the structure of fundi of the right and left eyes is left-right symmetric.
Hence, in fundus cameras, as disclosed in Japanese Patent Application Laid-Open No. S60-060831, Japanese Patent Application Laid-Open No. H06-217941, and Japanese Patent Application Laid-Open No. H09-271464, it has been performed up to now to present to a person to be examined a fixation target according to right and left eyes by providing an optical path which branches from an image sensing optical system, providing a plurality of light sources in conjugation positions with an image sensing plane in the optical path as fixation targets, and turning on the light sources selectively. Since image sensing light and a fixation target are visible light, a flip-up mirror, a half-mirror, or the like which branches an optical path is used.
In addition, what is also known is a method of Japanese Patent Application Laid-Open No. S51-137413 of arranging detachably a light source in an illumination optical system, and presenting a fixation target.
However, in the above-described conventional methods, there are problems that an optical system becomes large because of providing a branch optical path, and that a mechanism becomes complicated in the case of using a flip-up mirror, or a light source with a larger volume is needed since a utilization efficiency of light intensity falls in the case of using a half-mirror, and further, the dazzle of a person to be examined increases.
Furthermore, the method of arranging a light source as a fixation target in an illumination optical system has a problem that the image quality of a fundus observation image deteriorates since illumination unevenness arises because fundus illumination light is disturbed by parts for supporting the light source, the light source itself, a cable, and the like.